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Topic: 600 EX-RT for fill-in with burst : flash did not fire at each shot... (Read 4555 times)

First of all, let me introduce myself. I am French, I live in the French Alps close to Grenoble (the 1968 Winter Olympics city), and I have been a photography fan for many years.Since November 2012, I moved from Olympus 4/3rd DSLR to Canon Full Frame, with an Eos 5D mkIII body and some EF lenses. I shoot mainly wildlife, nature, landscapes and sports, but I intend to dig into portrait and social photography in the coming year.Two weeks ago, I got a Speedlite 600 EX-RT for my birthday with the ST-E3-RT trigger and an external Battery pack from Godox (Propac PB820).

I spent time to read the instruction manuals and to test this new gear at home. Yesterday, I went playing in the snow with my kids, and it was indeed an ideal case for my first “in real conditions” use. The weather was sunny (so, a lot of light with the white snow), and I wanted to try some fill-in.

Body was set to Av mode, auto ISO, center weighted metering, and equipped with the EF 70-200 f2.8L IS II. Flash was in E-TTL mode, high speed synchronization, and the external battery pack was plugged (Speedlite’s C.Fn 12 set to both inner batteries and external battery pack). I’ve been surprised to notice that when shooting 3 photos in bursts, the flash fired the first shoot, but not the following ones.

I thought that fill-in was indeed allowing burst with flash firing, and that adding an external battery pack would allow faster recycling to ensure even better flash firing at each shoot.I know that compensating the light due to snow and sunny ambiance requires some power, but I am a bit disappointed here. Is it the settings of my gear, or shall I consider that this case was a bit “extreme” for a first “in real conditions” ? Could you advise me ?

Another question : why, when using a Speedlite with the body in auto ISO, the ISO automatically sets to 400 ?

Flash was in E-TTL mode, high speed synchronization, and the external battery pack was plugged (Speedlite’s C.Fn 12 set to both inner batteries and external battery pack). I’ve been surprised to notice that when shooting 3 photos in bursts, the flash fired the first shoot, but not the following ones.

Hmmm, even with full power it *should* fire more than one if your battery pack is up to it and properly connected (which the flash doesn't show, mind you). You are shooting at worst-case conditions: hss, fill in snow (= fast shutter speeds = full flash burst). To debug, try shooting at a lower flash output with low fps. And don't forget sooner or later the flash overheats and stops flashing bursts.

Another question : why, when using a Speedlite with the body in auto ISO, the ISO automatically sets to 400 ?

Because Canon has a completely braindead auto iso function with flash as you just experienced ... the only way around this is to use Magic Lantern, it has an independent auto iso that works all the time.

As you state, fill in bright light needs more power...but HSS needs more power, too. You were in Av mode, but didn't mention the shutter speeds you were getting. If you were shooting at wide apertures, with sunlit snow I assume they were quite fast...HSS uses even more power as shutter speed increases. Regarding power loss from HSS, Canon states:

Quote from: Canon

The increased duration of the flash comes at the expense of the flash power, and the faster the shutter speed used, the lower the power. At a shutter speed of 1/500 second, the guide number of the Speedlite is less than half its normal rating, and this drops to less than a quarter at 1/2000 second.

I think the default is ISO 400 with flash and Auto ISO as a compromise between increased sensitivity (to make flash more efficient) and low noise. Obviously, you can select any specific ISO setting you wish with flash, if you don't use Auto.

Then why is it iso 400 on all cameras (crop, ff) and what about the famed high iso capability trumping the Nikon low iso trolls :-p ?

Really, there's no excuse I could imagine for this broken auto iso giving the user no options at all. The ML implementation shows that auto iso with flash works just fine w/o a single problem, I've been using it a lot since years from iso 100 to 6400 with m or ettl, local or remote, optical or radio... either there are historic reasons for the flash lockdown or of course configurations or situations I'm not aware of. The power output level is no reason though.

Then why is it iso 400 on all cameras (crop, ff) and what about the famed high iso capability trumping the Nikon low iso trolls :-p ?

Really, there's no excuse I could imagine for this broken auto iso giving the user no options at all.

Canon seems to start with green square mode, and go from their. When do 'most people' use flash? When the scene is dark. If you meter for ambient in dim light, with default settings and Auto ISO, the ISO will go pretty high - ISO 3200 on many cameras. That's not too noisy on my 1D X, but there's no question that it's noisier than ISO 400. At ISO 100, you are using a lot of flash power - 2-stops more than ISO 400, by definition.

The point is, if you're using auto-anything, you're trusting the camera to make decisions for you. In many situations, ISO 400 is quite a good compromise between flash power and image noise and DR.

In many situations, ISO 400 is quite a good compromise between flash power and image noise and DR.

No doubt, but it certainly is not the only compromise... I even went to the length to improve the Magic Lantern auto iso module myself because I'm usually using fill flash for backlit wildlife, and it's a blessing to have the camera choose iso 100 when possible or higher iso when necessary respecting a min. shutter speed.

I'm really wondering what the reason for the iso 400 lockdown is, my money is on firmware conservatism like the missing min. iso with older cameras or ec in m (tba on the 1dx in 2014 as I read), but then again I might be missing something.

@ both Marsu42 and Neuroanatomist :Thank you for your detailed answers.If I follow (and understand) you, my case is really extreme. Indeed, I tried to keep aperture at f2.8 or f4.0, resulting in speeds over 1/2000 - 1/4000 s. Such speeds do not always allow the flash condenser to refill, even with an external battery pack (by the way, all flash batteries and battery pack were freshly and fully charged). I should have probably set the ISO at 100 or even at the low extension (at 50), to decrease the power needed from the flash for fill-in. Maybe should I have set the flash to manual and set a low power (1/128, 1/64 or 1/32 max), as the purpose was to fill-in the shadows on the kids' faces and quite dark snow clothes.

And I understand from the debate I generated that this ISO auto = ISO 400 is clearly a feature stressing Canon users...

Thank you again, and any additional comment to advise would be fairly welcome

Such speeds do not always allow the flash condenser to refill, even with an external battery pack (by the way, all flash batteries and battery pack were freshly and fully charged).

I wouldn't say your case is extreme, but one good hint: If you know your flash is maxed out anyway, switch from ettl to full m flash mode because you're saving the power from the ettl preflash for the main flash... it's not much, but every bit helps.

Last not least, if you plan to shoot like this more often, use *two* flashes, reducing recycle times and extending the flash lifetime which severely degrades at 100%, my 600rt just died after 1.5 years (it's repaired on warranty though).

If I follow (and understand) you, my case is really extreme. Indeed, I tried to keep aperture at f2.8 or f4.0, resulting in speeds over 1/2000 - 1/4000 s. Such speeds do not always allow the flash condenser to refill, even with an external battery pack (by the way, all flash batteries and battery pack were freshly and fully charged). I should have probably set the ISO at 100 or even at the low extension (at 50), to decrease the power needed from the flash for fill-in. Maybe should I have set the flash to manual and set a low power (1/128, 1/64 or 1/32 max), as the purpose was to fill-in the shadows on the kids' faces and quite dark snow clothes.

And I understand from the debate I generated that this ISO auto = ISO 400 is clearly a feature stressing Canon users...

Thank you again, and any additional comment to advise would be fairly welcome

Even the 600EX-RT is very limited in HSS at 1/4,000. You have run into a hard limit. Changing iso would not help, if you lower iso the flash needs to output more power, which it can't do, if you lower the shutter speed you need to close the aperture (to maintain ambient) which will need the same flash power. If you raised iso then the flash would not have to work so hard, but again you'd have to close the aperture and that would take back the power you gained. If you used a ND filter to get you down to sync speed you would gain a stop or so of power that is intrinsically lost to HSS, but most of your gained power from lowering shutter speed would be used overcoming the darker scene and AF can be an issue.

We all know of the exposure triangle, aperture-shutterspeed-iso, most of us know the secondary flash exposure triangle, flash power and distance-aperture-iso. What many of us fail to take into account is when you go to HSS the shutter speed comes into the flash exposure triangle, wrecking it, and making a flash exposure square. At below sync speed the flash exposure is not impacted by the shutter speeds duration, all the flash is spent while the shutter is open, but in HSS the flash pulses, it pulses at the same rate at 1/8000 as at 1/300, obviously at 1/300 it gets 26 times more potential pulses than at 1/8000.

You have several options. Get the flash closer to the subject. Increase flash power, obviously that means another flash, but this will only give you one extra stop of light and is expensive. You can move location, that is find an area with less ambient, some open shade or a different time of day, not necessarily convenient. You can create your own shade, use a scrim, a sheet, an umbrella etc to put your subjects in shade, this is the most often used commercial technique, this has the added benefit of lowering the contrast across the subject so reducing the need for balancing flash, but again is not always convenient.

« Last Edit: December 09, 2013, 03:45:24 PM by privatebydesign »

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Too often we lose sight of the fact that photography is about capturing light, if we have the ability to take control of that light then we grow exponentially as photographers. More often than not the image is not about lens speed, sensor size, MP's or AF, it is about the light.

... I understand from the debate I generated that this ISO auto = ISO 400 is clearly a feature stressing Canon users...

Some of them, apparently.

Probably some of those who are still stuck to auto iso 400 with flash :-p ... if everybody else is fine with that they've got that certainly doesn't bother me.

I'm certainly struggling to get used to the flash settings.

But clearly it is possible to use flash at high ISO. Sometimes mine goes to 6400. And produces great reslts most of the time.

I'm not complaining as I suspect with my understanding of flash the camera is helping me.

I'm not one of those who will automatically assume that the camera is "crippled" or "broken" when it is restricted in some way. I start with the assumption that Canon know a lot more about making cameras than I do.

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If you debate with a fool onlookers can find it VERY difficult to tell the difference.

I start with the assumption that Canon know a lot more about making cameras than I do.

That's the spirit, I'll remember to nominate you for the "Canon compliance of the year" award :-p ... but you're correct, not every design decision is "crippling", but as it happens this one is different because ML has proven that auto iso with flash is no problem at all - you can use other iso settings manually, so there is really no reason why the camera shouldn't be able to select the iso according to the ambient light as usual and then let ettl decide the rest.

Even the 600EX-RT is very limited in HSS at 1/4,000. You have run into a hard limit. Changing iso would not help, if you lower iso the flash needs to output more power, which it can't do, if you lower the shutter speed you need to close the aperture (to maintain ambient) which will need the same flash power. If you raised iso then the flash would not have to work so hard, but again you'd have to close the aperture and that would take back the power you gained. If you used a ND filter to get you down to sync speed you would gain a stop or so of power that is intrinsically lost to HSS, but most of your gained power from lowering shutter speed would be used overcoming the darker scene and AF can be an issue.

I would have thought that reducing ISO would involve increasing exposure time, i.e. Decreasing shutterspeed to an output less than 1/1000s, potentially more favorable to HSS. But I don't understand why it would involve the flash needing more power, knowing I was quite close to my kids (about 3 meters). I am certainly not an expert, but I assume the distance is also of importance to determine the needed power when using E-TTL. Am I wrong ?

I did not want to close the aperture, but the bckground being only snow, it would have not been a real issue. I should have tried it. But my initial purpose was indeed to blur the background, which is the reason to use HSS primarily. So I remained at f2.8 or f4...